Cognitive memory and habit formation are two qualitatively different learning processes based on separate neural systems, a cortico-limbic and a cortico-striatal system, respectively. To see how emotional and social behavior develop in the absence of cognitive memory (i.e., in the presence of a global amnesia that persists from infancy through adulthood) we prepared monkeys with neonatal limbic lesions and followed their behavioral development. Animals with neonatal removal of cortical area TE, a higher- order visual station linked to both learning systems, serve as controls. Interestingly, although early damage to the limbic memory system did not yield the Kluver-Bucy symptoms of loss of fear, indiscriminate approach to objects, and coprophagy, seen in monkeys given limbic lesions in adulthood, it produced other behavioral abnormalities, such as lack of social interactions, blank facial expression, and motor stereotypies. The developmental time course and the nature of these disturbances resemble those seen in autistic children. Assessment of the effects of the neonatal lesions on the early development of habits and memories points to greater compensatory potential after neonatal cortical than after neonatal limbic removals, suggesting that cortical association areas are relatively immature at birth. Direct evidence of neocortical immaturity in the macaque has been provided by our neurobiological studies on opiatergic and cholinergic receptor distribution and on metabolic activity. Data on both normal and operated infants suggest that development of the cortico- neostriatal habit system is sexually dimorphic, and that this is due to the high testosterone levels present in male infants before and shortly after birth. Finally, studies in young adult monkeys together with those in normal aged animals are providing the anatomical and chemical basis for understanding the memory disorders in humans that accompany cerebrovascular and other cerebral accidents and diseases as well as the gradual decline in memory ability that occurs with normal aging.